198 Wortman — Studies of Eocene Mammalia in the 



The type of L. riparius, having but two subequal lower 

 molars, was otherwise unknown, and was regarded as a distinct 

 genus. The relationship with Oxycenodon was entirely over- 

 looked. The unstudied part of the collection affords much 

 additional material, and it is now quite evident that the number 

 of superior molars in L. verus is two instead of three. The 

 association of upper and lower teeth in this material renders 

 it clear, moreover, that the type of L. riparius is the lower 

 jaw of L. vents, and on this account I do not hesitate to unite 

 them. I also arrange Thinocyon and Oxycenodon in this 

 genus, but, as already remarked, it may be found, with more 

 complete information, that they represent distinctive generic 

 modifications. 



Limnocyon verus Marsh. 

 Limnocyon verus Marsh, this Journal, 1872, p. 6, Separata. 



Originally established upon a superior series of teeth of the 

 right side, figure 71, with the first premolar only, in place. 



71 



Figure 71. — Series of right superior teeth of Limnocyon verus Marsh ; 

 crown view ; three halves natural size. (Type.) 



The two middle incisors are present, but they do not present 

 any characters of unusual importance ; their roots are much 

 compressed from side to side, like certain members of the 

 Mustelidse, and their crowns are obtusely pointed and rather 

 narrow. The canine is represented by fragments only, but 

 these are sufficient to indicate that it had the usual size and 

 form of this tooth among the Carnivora ; its surface is traversed 

 by characteristic longitudinal grooves and ridges, much as in 

 certain species of reptiles. There are apparently no traces of 

 these grooves and ridges upon the canines of the other species 

 of the genus (except very faint ones in L. velox), and it may 

 be taken to be diagnostic. 



The first premolar is two-rooted, with a conical, more or less 

 recurved, principal cusp, and a rather extended heel bearing a 

 small cusp ; it is placed immediately behind the canine without 

 the intervention of a diastema. The second premolar is only 

 partially preserved in the type, but is present in many other 

 specimens in the collection. The third premolar is missing in 



